Unipolar Resistive Switching Behavior Research Articles

Unipolar resistive switching behavior in sol–gel synthesized FeSrTiO3 thin films

A robust and reproducible resistance switching in iron substituted strontium titanate is reported which shows giant high to low resistance state ratio (∼105) and stable charge retention.

Effects of electrode on resistance switching properties of ZnMn2O4 films deposited by magnetron sputtering

ZnMn2O4 films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn2O4 films were investigated. The ZnMn2O4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn2O4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn2O4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest RHRS/RLRS ratio of 104 and the lowest VON and VOFF of 3.0 V have been observed in Ag/ZnMn2O4/Pt device. Though the Ag/ZnMn2O4/n-Si device also possesses the highest RHRS/RLRS ratio of 104, but the highest values of VON,VOFF, RHRS and RLRS, as well as the poor endurance and retention characteristics.

Unipolar resistive switching behavior of amorphous SrMoO4 thin films deposited at room temperature

Amorphous SrMoO4 (SMO) thin films were deposited on Pt/Ti/SiO2/Si substrates at room temperature by pulsed laser deposition and the resistive switching (RS) behavior of the Au/SMO/Pt devices was investigated. The Au/SMO/Pt devices exhibit typical unipolar RS behavior with excellent switching parameters as follows: high resistance ratio (~105) between the low resistance state (LRS) and high resistance state (HRS), non-overlapping switching voltages, and good endurance and retention characteristics. Detailed analysis of their current-voltage characteristics reveals that the conduction mechanisms are Ohmic conduction in the LRS and lower voltage region of HRS, and Poole-Frenkel emission in the higher voltage region of the HRS. Temperature dependent resistance measurements, combined with x-ray photoelectron spectroscopy and model analysis indicate that the unipolar RS behavior of the Au/SMO/Pt devices could be understood by a conical conducting filaments (CFs) model in which the conical CFs are composed of oxygen vacancies. The conical CFs extend from the cathode to anode during the forming process and the observed RS behavior occurs in the localized region near the anode. These results suggest that the room-temperature- deposited amorphous SMO thin films could find potential application in nonvolatile RS memory.

Coexistence of bipolar and unipolar resistive switching characteristics of thin TiO2 film grown on Cu foil substrate for flexible nonvolatile memory device

This work reports the coexistence of bipolar and unipolar resistive switching behaviors in the flexible Ni/TiO2/Cu device. The amorphous TiO2 thin film was deposited by radio frequency magnetron sputtering method on flexible copper (Cu) foil substrate at room temperature. The resistive switching behaviors of the flexible device were slightly degraded upon different bending states, indicating the huge potential applications in the flexible electronics. The switching mechanism based on conducting filaments is proposed to explain the resistive switching behaviors.

Unipolar resistance switching behavior of Pr4O7-Pr2CuO4-δ thin films

Pr4O7-Pr2CuO4-δ (PCO) thin films were grown on Pt (Pt/Ti/SiO2/Si) substrates by pulsed laser deposition and their resistive switching behavior was investigated. The resistance ratio RH/L (Rhigh/Rlow) could be larger than 104, which can be maintained up to 50cycles and 104s without detectable degradation. The results show that the Pt/Pr4O7-PCO/Pt device possesses excellent endurance and retention properties. The physical mechanism of resistive switching in Pr4O7-PCO film could be ascribed to the forming and rupturing of conductive filaments via migration of oxygen vacancies.

Parameters controlling microstructures and resistance switching of electrodeposited cuprous oxide thin films

Cuprous oxide (Cu2O) thin films were electrodeposited cathodically from a highly alkaline bath using tartrate as complexing agent. Different microstructures for Cu2O thin films were achieved by varying the applied potential from −0.285 to −0.395V versus a reference electrode of Ag/AgCl at 50°C in potentiostatic mode, and separately by changing the bath temperature from 25 to 50°C in galvanostatic mode. Characterization experiments showed that both grain size and orientation of Cu2O can be controlled by changing the applied potential. Applying a high negative potential of −0.395V resulted in smaller grain size of Cu2O thin films with a preferred orientation in [111] direction. An increase in the bath temperature in galvanostatic electrodeposition increased the grain size of Cu2O thin films. All the films in Au/Cu2O/Au-Pd cell showed unipolar resistance switching behavior after an initial FORMING process. Increasing the grain size of Cu2O thin films and decreasing the top electrode area increased the FORMING voltage and decreased the current level of high resistance state (HRS). The current in low resistance state (LRS) was independent of the top electrode area and the grain size of deposited films, suggesting a filamentary conduction mechanism in unipolar resistance switching of Cu2O.

Nonvolatile conductive filaments resistive switching behaviors in Ag/GaO x /Nb:SrTiO3/Ag structure

Ag/GaOx/NSTO/Ag structures were fabricated, and the electrical properties measurement results show that the device behaviors a unipolar resistance switching characteristic with bi-stable resistance ratio of three orders. In the positive voltage region, the dominant conducting mechanism of high resistance state obeys Poole–Frenkel emission rules, while in the negative region, that obeys space-charge-limited current mechanism. Both the I–V curves of ON and OFF states and temperature-dependent variation resistances indicate that the unipolar resistance switching behavior can be explained by the formation/rupture of conductive filaments, which composed of oxygen vacancies. The stable switching results demonstrated that the structure can be applied in resistance random access memory devices.

Thickness effect on the stability of unipolar resistance switching in tin ferrite thin films

We report the reproducible unipolar resistance switching behavior in Pt/SnFe2O4/Pt structures. The amorphous SnFe2O4 thin film was spin-coated on the Pt/TiO2/SiO2/Si substrate by a sol-gel method. The current-voltage characterization showed that as the spin coating cycles increased, the resistive switching (RS) characteristics became stable, and an excellent RS performance showing uniform set voltage distribution, stable resistance of both low resistance and high resistance states, and narrow reset current distribution can be obtained in SFO films with a thickness about 220 nm. Based on the conducting filament model, the variation of the RS behavior was ascribed to the increase of the electroforming voltage in the thicker films, which consequently induced more oxygen vacancies to participate in the RS process. Our results indicated that the electroforming voltage performs a significant role in the RS properties of the amorphous SnFe2O4 and the optimized RS behavior through the regulation of preparation process can be used for the resistance random access memory applications.

Electrical Properties and Nanoresistive Switching of Ni-HfO2-Si Capacitors

Ni/HfO2/Si ReRAM devices were extensively characterized. In the pristine state, they show adequate performance with low leakage currents and moderate interfacial state density. Leakage current is dominated by Poole-Frenkel mechanism. Activation energies of conduction processes and soft-optical phonons in the insulator bulk are 80 and 50 meV, respectively. Both are usual values in high-k dielectrics. Devices show unipolar resistive switching behavior, with two well-defined resistance states. They can switch properly at temperatures as low as 77 K. Transitions between both resistance states are electric field and temperature dependent.

Forming-free unipolar resistive switching behavior with conical conducting filaments in LaVO4 thin films

LaVO4 thin films have been deposited on Pt / Ti /SiO2 /Si substrates by pulsed laser deposition in order to explore the resistive switching (RS) behavior of the Au/LaVO4/Pt devices. It is found that the as-prepared Au/LaVO4/Pt devices stay in the low resistance state (LRS) and no electroforming process (forming-free) is needed to trigger fresh devices for the subsequent RS. Furthermore, the devices show excellent switching parameters such as a reproducible switching effect, a high resistance ratio of ∼104 between the LRS and high resistance state (HRS), good endurance and retention characteristics, and non-overlapping switching voltages. The dominant conduction mechanisms are Ohmic conduction in the LRS and the lower voltage region of the HRS, and Poole–Frenkel emission in the higher voltage region of the HRS. The combination of temperature dependence of resistance, x-ray photoelectron spectroscopy, and model analysis suggests that the forming-free unipolar RS behavior can be explained by the formation and rupture of conical conducting filaments formed out of oxygen vacancies. These results may be important for practical application in nonvolatile resistive switching memory.

Reversible transition between bipolar and unipolar resistive switching in Cu2O/Ga2O3 binary oxide stacked layer

Both unipolar resistive switching (URS) and bipolar resistive switching (BRS) behaviors are observed in Cu2O/Ga2O3 stacked layer. The conversion between BRS and URS is controllable and reversible. The switching operations in BRS mode requires smaller voltage than that in the URS mode. The oxygen vacancies closed to the Cu2O/Ga2O3 interface contributes to the BRS, and the bias-controlling filament formation/rupture in depletion layer is considered to contribute to the URS. The URS happens only in the negative voltage part due to the nature of directionality of the p-n junction. The process reported here can be developed to design memory device.

Unipolar resistive switching behaviour of copper doped polyvinyl alcohol/lead sulphide quantum dot device

Copper doped lead sulphide quantum dots (PVA/PbS:Cu) with 0.5 and 1 % Cu dopant concentration were synthesized by chemical route. Structural, chemical and optical characterizations viz., X-ray diffraction study, UV–visible spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, selected area electron diffraction were done to confirm nanoformation in the as-synthesized copper doped lead sulphide samples. Significant changes in structural, optical and electrical properties of the as-fabricated samples were observed with variation in percentage of copper dopant concentration. I–V characteristics of the as-fabricated AL/PVA/PbS:Cu QD/ITO devices with the PVA/PbS:Cu samples as the active layer of the devices, exhibits unipolar resistive switching characteristics with ROFF/RON ratio of ~102 and ~103. Variation in the ROFF/RON ratios of investigated devices with different copper dopant concentrations points towards possibility of designing AL/PVA/PbS:Cu QD/ITO devices with different ROFF/RON ratios by varying Cu dopant concentration.

Coexistence of bipolar and unipolar resistive switching behaviors in the double-layer Ag/ZnS-Ag/CuAlO2/Pt memory device

The coexistence of uniform bipolar and unipolar resistive-switching (RS) characteristics was demonstrated in a double-layer Ag/ZnS-Ag/CuAlO2/Pt memory device. By changing the compliance current (CC) from 1mA to 10mA, the RS behavior can be converted from the bipolar mode (BRS) to the unipolar mode (URS). The temperature dependence of low resistance states further indicates that the CFs are composed of the Ag atoms and Cu vacancies for the BRS mode and URS mode, respectively. For this double-layer structure device, the thicker conducting filaments (CFs) will be formed in the ZnS-Ag layer, and it can act as tip electrodes. Thus, the formation and rupture of these two different CFs are located in the CuAlO2 layer, realizing the uniform and stable BRS and URS.

Filament Geometry Induced Bipolar, Complementary, and Unipolar Resistive Switching under the Same Set Current Compliance in Pt/SiOx/TiN.

The decidedly unusual co-occurrence of bipolar, complementary, and unipolar resistive switching (BRS, CRS, and URS, respectively) behavior under the same high set current compliance (set-CC) is discussed on the basis of filament geometry in a Pt/SiOx/TiN stack. Set-CC-dependent scaling behavior with relations Ireset ~ R0–α and Vreset ~ R0–β differentiates BRS under low set-CC from other switching behaviors under high set-CC due to a low α and β involving a narrow filamentary path. Because such co-occurrence is observed only in the case of a high α and β involving a wide filamentary path, such a path can be classified into three different geometries according to switching behavior in detail. From the cyclic switching and a model simulation, we conclude that the reset of BRS originates from a narrower filamentary path near the top electrode than that of CRS due to the randomness of field-driven migration even under the same set-CC. Also, we conclude that URS originates from much narrower inversed conical filamentary path. Therefore, filament-geometry-dependent electric field and/or thermal effects can precisely describe the entire switching behaviors in this experiment.

Resistive Switching Characteristics of Atomic-Layer-Deposited Y2O3 Insulators with Deposition Temperature.

Resistive switching characteristics of insulating Y2O3 films grown by an atomic layer deposition technique have been investigated with their growth temperature range of 250 °C to 350 °C. Ru/Y2O3/Ru resistors reveal the bi-stable unipolar resistive switching behaviors. Resistive switching behaviors are related to the chemical bonding states of Y2O3 insulating films. As the insulating film growth temperature increases, Y2O3 film becomes much stoichiometric and little contaminated with impurities. Moreover, the resistance ratio high resistance state to low resistance state increases at growth temperature over 300 °C.

Possible application of lead sulfide quantum dot in memory device

Abstract Unipolar resistive switching behavior was observed in the as-fabricated Al/PVA/PbS QD/ITO device with R OFF/R ON ratio of 3.15×103 with retentivity for prolonged time and repeatability of hysteresis loops. Schottky emission mechanism dominates conduction mechanism in low-resistance state and high-resistance state of the device. Unipolar resistive switching behavior observed in the device is attributed to Coulomb blockade. The observed characteristic in the device points toward possible application of PbS QDs in memory device.

Coexistence of bipolar and unipolar resistive switching in Al-doped ceria thin films for non-volatile memory applications

The Ti/CeO2/Al/CeO2/Pt stacks as a ReRAM device exhibits bipolar and unipolar resistive switching behaviors. The OFF/ON resistance ratio (>102) in both modes is almost similar but operating voltages are slightly smaller in the former than in the later. These devices could switch between the two operating modes merely by choosing the polarity of RESET voltage. In addition, the requirement of identical current compliance during the SET process of both modes provides an additional advantage of simplicity in device operation. The conduction mechanisms of high resistance state and low resistance state are Schottky emission and Ohmic conduction. On the basis of analyses of current–voltage characteristics and temperature dependence of resistance, resistive switching mechanism originated from a combined effect of field induced diffusion of oxygen and Al ions in the sandwiched ceria matrix.

The effect of Cu doping concentration on resistive switching of HfO2 film

The Cu-doped and undoped HfO2 films were fabricated and the effect of Cu doping concentration on resistive switching (RS) of HfO2 film was demonstrated. The X-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical bonding states of Cu in HfO2:Cu film. The improved RS behaviors in terms of ON/OFF ratio and switching parameters were observed for Cu-doped HfO2 film with bipolar resistive switching (BRS) behavior. With the increase of Cu doping concentration, the 9.7% Cu-doped HfO2 film showed both BRS and unipolar resistive switching (URS) behaviors with large operating voltages. The space charge limited current (SCLC) effect was proposed to interpret the switching mechanism of HfO2:Cu films with BRS behavior and the URS behavior can be explained by the migration of Cu ions.

Initial defect configuration in NiO film for reliable unipolar resistance switching of Pt/NiO/Pt structure

We report on an oxygen partial pressure dependence of the unipolar resistance switching behavior of a Pt/NiO/Pt structure. By varying the oxygen partial pressure from 1 to 50 mTorr during film growth, we observed the reliable resistance switching behaviors in the films grown at high oxygen partial pressure, whereas we observed a failure of resistance switching behavior for the film grown at low pressure. In situ x-ray photoemission spectroscopy revealed that the unipolar resistance switching behavior was observed prominently in the NiO film of almost bulk stoichiometry accompanying a considerable off-stoichiometry near the NiO–Pt interface. Based on these observations, we extend the understanding of the effect of the initial defect configuration on the reliability of resistance switching in the Pt/NiO/Pt structure.

Nonvolatile unipolar resistive switching behavior of amorphous BiFeO3 films

Amorphous BiFeO3 thin films were grown on an indium tin oxide glass substrate using RF magnetron sputtering at room temperature. The resistive switching behavior of amorphous BiFeO3 thin films was investigated. The Au/amorphous BiFeO3/indium tin oxide device exhibited the stable unipolar resistive switching behavior with a substantial resistance ratio (larger than 102) between low and high resistance states and the excellent retention performance. The low resistance state exhibited a linear Ohmic behavior, while the high resistance state conduction could be ascribed to the trap controlled space-charge limited conduction mechanism. Based on the X-ray photoelectron spectroscopy, the observed resistive switching behavior was mainly attributed to the electric field induced migration of oxygen vacancies.